extractPreserveChunks() when string contains emoji unicode on Windows

[shrektan]

When the string contains emoji Unicode like "\U0001F937" on Windows , extractPreserveChunks() returns unexpected results.

It leads to an issue that when the user compiles an Rmd file with such Unicode strings on Windows, the htmlwidgets of the HTML output file after the line contains the emoji string, can't be displayed properly, e.g., rstudio/DT#661

The cause of this issue I believe is that gregexpr(perl = FALSE) (the default) can't handle such cases properly on Windows (I don't know the reason). By explicitly using perl = TRUE will fix this issue.

htmltools/R/tags.R

Line 1170 in e07546c

matches <- gregexpr(pattern, strval)[[1]]

R code to reproduce

x <- "<!--html_preserve-->chunck1<!--/html_preserve-->\U0001F937<!--html_preserve-->chunck2<!--/html_preserve-->"
htmltools::extractPreserveChunks(x)

The output

$value
[1] "preserve054aaf381ec98343\U0001f937<preserve86252470130ed05d"

$chunks
preserve86252470130ed05d preserve054aaf381ec98343 
               "hunck2<"                "chunck1" 

The session info

R version 3.6.2 (2019-12-12)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 10 x64 (build 17763)

Matrix products: default

locale:
[1] LC_COLLATE=Chinese (Simplified)_China.936 
[2] LC_CTYPE=Chinese (Simplified)_China.936   
[3] LC_MONETARY=Chinese (Simplified)_China.936
[4] LC_NUMERIC=C                              
[5] LC_TIME=Chinese (Simplified)_China.936    

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] shiny_1.4.0

loaded via a namespace (and not attached):
 [1] Rcpp_1.0.3      rstudioapi_0.11 knitr_1.28      whisker_0.4    
 [5] magrittr_1.5    xtable_1.8-4    R6_2.4.1        rlang_0.4.2    
 [9] fastmap_1.0.1   tools_3.6.2     xfun_0.12       miniUI_0.1.1.1 
[13] clipr_0.7.0     htmltools_0.4.0 digest_0.6.23   processx_3.4.2 
[17] callr_3.4.2     later_1.0.0     fs_1.3.1        promises_1.1.0 
[21] ps_1.3.0        evaluate_0.14   mime_0.8        rmarkdown_2.1  
[25] reprex_0.3.0    compiler_3.6.2  jsonlite_1.6    httpuv_1.5.2 

[cpsievert]

It appears that the perl = TRUE change in #157 didn't fix this for any version of perl on windows. https://github.com/rstudio/htmltools/runs/750362532#step:12:284